They are from the United States.我可以写成这样吗?They are from the United States.如果这样写对吗？They be from the United States.

They are from the United States.我可以写成这样吗?They are from the United States.如果这样写对吗？They be from the United States.
They are from the United States.我可以写成这样吗?They are from the United States.
如果这样写对吗？They be from the United States.

They are from the United States.我可以写成这样吗?They are from the United States.如果这样写对吗？They be from the United States.
They are from the United States.这个对,但是用be就错了.
我想你问的主要是主语和be动词谓语的搭配问题.I用am,过去时was.you和they用are,过去用were.it和she和he都用is,过去用was.
用be的情况一般只有是将来时,用will be.
如：I will be there on time.我会准时到那里的.
She will be the queen.她将会成为皇后.

可以

正确 另一种写法是：
They come from the United States

很对啊！主谓语都全了，语法也很对。就像I am from China